Coated article comprising a substrate of polyethylene or polyamide and a grafted coating of polytetrafluoroethylene or polymethyl methacrylate



Sept. 12, 1961 E. Bu ETAL L2,999,772

R. .A COATED ARTICLE COMP A SUBSTRATE OF POLYETHYLENE OR POLYAMI AND A GRAFTED COATING OF POLYTETRAFLUOROETHYLENE 0R POLYMET-IYI.. METHACRYLATE Filed NOV. 6, 1952 GRAFT COATING SUBSTRATE N E V \GRAFT COATING GRAFT COATING SUBSTRATE INVENTORS ROBERT E. BURK EDWARD H. PRICE BY uzgm.

ATTORNEY CATED AR'HCLE 'COMPRSlNG A. SUBSTRA'IE F PLYEHYLENE 0R PLYv 1i I' E AND A CATHNG F PLYTETRAFLUR- E'EHYLENE @R PULYMSETHYL METHACRY- Robert E. Burk and Edward H. Price, West Chester, Pa., assigner-s to E. l. du Pont de Nemours and. Company,

Wilmington, Del., a corporation of Delaware Filed Nov. 6, 1952, Ser. No. 319,134

2 Claims. (Cl. 117-138.@

This invention relates to a process for chemically attaching one polymeric substance to another. More specically, this invention relates to a process for grafting polymeric materials such as polymetnyl methacrylate, polytetralluoroethylene, etc. onto a different polymeric material; for example, polyethylene, nylon, etc.

Just as the properties of steel and other alloyshave been altered by additions of other substances, so have the characteristics of plastic materials been changed to meet various new uses by the addition or" other substances. Thus, in the rubber industry many mixtures or" rubber and other polymerizable substances have been made to meet the demands of the public. Copolymerization, interpolymerization, plasticization, stabilization, and the like are some of the means by which the plastic industry has altered the physical and chemical properties of plastic materials.

in the plastic industry, synthetic materials are being discovered, blended, and perfected constantly in order to develop materials which can replace metals, wood, animal and vegetable products, etc. so as to conserve our natural resources, and to produce a satisfactory and economical replacement. Any one polymeric substance may have certain desirable characteristics such as weight, toughness, hardness, tensile strength, and others, but an attempt to obtain two or more of these properties in a single material is often very difficult. As a result, blends of two or more substances may be utilized, but this procedure often has the eifect of producing a material carrying over none of the strong characteristics of the ingredients of the blend, but rather a series of characteristics blanketing each other so that no one or two are dominant. For example, a mixture of Compound A having a high tensile strength and Compound B having a high dielectric strength may be blended to produce a material having merely ordinary tensile strength and ordinary dielectric strength.

By means of laminating layers of different materials, each having certain desirable properties, a composite substance may be produced which has many desirable properties. The disadvantage of laminates is the inherent incorporation of an adhesive which may or may not detract from the usefulness of the iinal composite structure.

lt is an object of this invention to alter the characteristics of a plastic material by grafting one polymer to another polymer by means of a process which is capable of attaching one polymeric substance to another without the aid of an adhesive. By this process, itis possible to cover a base material of high physical strength with a material of high dielectric strength and thus produce a composition having both desirable properties in yan undiluted form, and without the inclusion of a layer of Vadhesive material which might break loose or impart other undesirable properties.

it is another object of this invention to provide a process for polymerizing a monomeric material in the presence of a solid polymeric substance, chemically distinct from said monomeric material, in such a fashion that said monomeric material is polymerized and, at the same time, is attached or grafted to said polymeric substance.

2,999,772 Patented Sept.. l2, i961 It is another object of this invention to alter the surface characteristics of a polymeric substrate by forming surface coating of a different polymer grafted onto the substrate. Y

Other objects will appear in the detailed description given hereinafter. The following examples are set forth to more adequately describe the process of this invention.

in the attached drawings there are graphic illustrations of certain embodiments of this invention. FIGURE l shows a section through a film, sheet, or the like in which the central substrate has been covered on each side with a graft coating. FIGURE 2 shows a tubular article in which the inside and outside surfaces of the tubular substrate have been covered with a graft coating. FIGURE 3 shows a portion of `a rod-like structure fwith the substrate covered with a graft coating.

Example 1 A sheet of polyethylene, approximately 4 mils thick, was placed into a `stainless steel lined horizontal shaker tube of 325 ml. capacity. There was also introduced into the shaker tube, 1 gram of ammonium peruoroc-arboxylate (made from C8 and C9 perlluorocarboxylic acids), 0.02 gram of ammonium persulfate, 200 ml. demineralized water and suiiicient tetralluoroethylene to impart a pressure of 300 p.s.i. inside the tube. The tube was sealed and shaken at a temperature of 78-80 C. for a period of 54 minutes at continued pressures of about 280-300 p.s.i. internal pressure of the shaker tube was relieved, the seal broken, and the strip of polyethylene was removed.

Physical examination of the polyethylene strip removed from the shaker tube showed a thin lm of polytetraduoroethylene grafted onto the polyethylene. Approximately 0.5% weight increase was obtained due to the polytetrafluoroethylene. To the naked eye the polyethylene appeared to be frosted, and under a thermal microscope using polarized light the polytetrailuoroethylene was seen to be present as a thin coherent coating. Both surfaces of the polyethylene strip were equally well covered, and there was no evidence ofpenetration of the polytetrailuoroethylene into the polyethylene.

The same experiment was run using polyethylene tubing. The tubing was coated with a thin layer of poly- Example 2 A strip of polyhexamethylene adipamide, 15 mils thick, having a number average molecular weight of 10,000- 40,G00, was placed in a horizontal platinum-lined shaker tube of 325 capacity. The tube was charged with 200 ml. of Water, 0.02 gram of ammonium persulfate and sufficient monomeric tetratluoroethylene to impart an internal pressure of 300 p.s.i. to the sealed tube at 65 C. The tube was shaken at 65 C. for l5 minutes, and thereafter at 82-85 C. for 5l minutes, during which time the pressure was maintained at 300 psi. by the addition of tetraliuoroethylene. T he polyamide film was coated evenly and lirmly with polytetrauoroethylene. The coating v by 1A; inch. The coating obtained on the bar had exactly i the same characteristics as described above in relation to the polyamide lm.

Example 3 A one-liter resin ask was iitted for evacuation, introduction of monomer, receiving a manometer connection, and receiving a thermometer. A strip of polyethylene, approximately 5 mils thick, was treated with benzoin. The benzoin treatment consisted of evaporating 1 ml. of a 1% solution of benzoin in alcohol on 25 sq. in. of a polyethylene lm. This procedure gave a concentration of about 0.4 mg. Vof benZoin/sq. in. of tilm surface. A strip of this treated lm was suspended from a glass rack placed inside the resin iiask, after which, the flask was iilled with methyl methacrylate vapors. The pressure was maintained at 50 to 100 mm. and the temperature at 45 to 50 C. The necessary heat was supplied by an infrared lamp directed at the iiask. Ultraviolet light was used to promote polymerization of the methyl methacrylate. The ultraviolet light was supplied by two tubular fluorescent-type lights commonly known and sold as BL- 360 lights. The flask and its enclosed monomer and the treated ilm were irradiated for various lengths of times, and thereafter the film was removed from the iiask. When the iilm was folded and creased, neither the polyethylene substrate nor its grafted Icoating of polymethyl methacrylate cracked or separated from each other in any way.

In a series of experiments conducted as described above, polymethyl methacrylate iilms of 0.01 to 1.7 mils calculated from weight gain thickness were formed on the strip of polyethylene by ultraviolet irradiation varying from 5 to 200 minutes, respectively, at pressures of methyl methacrylate vapors of 40-60 mm.

In order to show that the polymethyl methacrylate was truly grafted to the polyethylene tilm, a strip irradiated for 135 minutes to produce a thick polymethyl methacrylate lm coating was subjected to a series of solvent extraction treatments consisting of firstly, soaking the coated polyethylene strip overnight in acetone at room temperature, secondly, immersing the strip in refluxing acetone for 6 hours, and lastly, digesting the strip with glacial acetic acid heated to 80 C. on a steam bath. There was only a negligible weight loss recorded after each of the three solvent extraction treatments described above. Furthermore, there was no change in the characteristic polymethyl methacrylate infrared pattern of the coated strip after each of the above-described solvent extraction steps.

It is known that polyethylene iilms, as well as many other film materials, have certain surface characteristics which prevent adjacent iilms from sliding over each other easily. This property is commonly known as slip. If two identical lms are laid face to face and can be moved in sliding relationship to each other while maintaining surface contact, the ilm is said to have good slip; and conversely, if the sliding motion is only accomplished with diiculty, and the surfaces seem to stick to each other, the tilm is said to have poor slip characteristics. Obviously, there are some uses of lms which require good slip and others which require poor slipf Untreated polyethylene is intermediate in its slip characteristics. When subjected to the sliding block test, untreated polyethylene lms have slip angles or" about 45 The process of this invention, when used to coat polyethylene with polymethyl methacrylate, produces coated polyethylene iilms having slip angles of 23 to 27.

It is not known exactly what is the method of attachment of the grafted coating to the substrate, however, the results show conclusively that there is more than a mere physical coating involved. Solvent extraction does not remove the grafted coating. Films of polyethylene having thereon a coating of polymethyl methacrylate produced according to this invention do not crack when folded and creased. New desirable surface characteristics are produced for the substrate. Thus this invention has produced an entirely new product and process which have wide application in the manufacture of plastic materials.

We claim:

l. A coated article comprising a solid, shaped, thermoplastic, synthetic polymeric substrate and a continuous coating of a thermoplastic, synthetic polymer grafted to said substrate, said article being selected from the group consisting of a polyethylene substrate coated with polytetrauoroethylene, a polyethylene substrate coated with polymethyl methacrylate, and a polyamide substrate coated with polytetraduoroethylene; said coated article being characterized in that the coating is incapable of being removed from said substrate when the coated article is subjected to the action of a compound which is a sol- Vent for the material comprising said coating and a nonsolvent for the material comprising said substrate.

2. A coated article comprising a solid, shaped substrate of polyethylene and a continuous coating of polymethyl methacrylate bonded to said substrate in such a fashion that the coating is unaiected by subjecting the coated article to the action of a solvent for polymethyl methacrylate.

References Cited in the file of this patent UNITED STATES PATENTS 2,028,776 Hibbert Ian. 28, 1936 2,320,533 Muskat June l, 1943 2,332,461 Muskat Oct. 19, 1943 2,406,454 Charlton Aug. 27, 1946 OTHER REFERENCES Journal of Polymer Science, vol. VIH, No. 3, pages 289-311, March 1952, presented at the International Congress of Pure and Applied Chemistry, New York, September 1951. 

1. A COATED ARTICLE COMPRISING A SOLID SHAPED, THERMOPLASTIC, SYNTHETIC POLYMERIC SUBSTRATE AND A CONTINUOUS COATING OF A THERMOPLASTIC, SYNTHETIC POLYMER GRAFTED TO SAID SUBSTRATE, SAID ARTICLE BEING SELECTED FROM THE GROUP CONSISTING OF A POLYETHYLENE SUBSTRATE COATED WITH TETRAFLUOROETHYLENE, A POLYETHYLENE SUBSTRATE COATED WITH POLYMETHYL METHACRYLATE, AND A POLYAMIDE SUBSTRATE COATED WITH POLYTETRAFLUOROETHYLENE, SAID COATED ARTICLE BEING CHARACTERIZED IN THAT THE COATING IS INCAPABLE OF BEING REMOVED FROM SAID SUBSTRATE WHEN THE COATED ARTICLE IS SUBJECTED TO THE ACTION OF A COMPOUND WHICH IS A SOLVENT FOR THE MATERIAL COMPRISING SAID COATING AND A NONSOLVENT FOR THE MATERIAL COMPRISING SAID SUBSTRATE. 